Moving Videos on Green Screen
How I would do it 

Your best bet for scaling, rotating, moving, and animating all that stuff would be through the VSE. 
1. In the compsitor remove the green background to make adding the background easier later on using the keying node. 
2. Open blenders VSE and add in your newly rendered transparent video through SHIFT+A > movie 
3.With your clip selected add a transform strip via SHIFT+A > Effect Strips.. > transform. Once there you can change the size rotation and location all from the properties panel on the timeline. Your probably going to want to keyframe the movement of the tank so using the timeline put the timeline where wish and using the transformation strip you can change how the tank looks relative to the frame. Hover over the location, roation, and whatnot and then press "i" to keyframe it. 
4. After you render that run through the compsitor with an alpha over node and add your pic - that should do it. 

References 

https://www.youtube.com/watch?v=h0F5X4b7jug 
http://blenderartists.org/forum/showthread.php?261401-how-i-add-or-active-keyframe-for-VSE-blender 
https://www.youtube.com/watch?v=0PZ_cxjxexM